Compressed air supply system



Jan. 20, 1953 R. Mo 2,626,100

COMPRESSED AIR SUPPLY SYSTEM Filed Jan. 1'7, 1952 Figl.

is Attorney.

Patented Jan. 20, 1953 UNITED s'mrs TENT OFFICE COMPRESSED AIR SUPPLYSYSTEM Roger McIntyre, Erie, Pa., assignor to General Electric Company,a corporation of New York '7 Claims.

This invention relates to compressed air supply systems, and moreparticularly to an arrangement for unloading the compressor of such asystem for starting.

In the past, it has generally been the design practice on locomotives,for example, dieseleleotric and gas turbine-electric locomotives, todirect-connect the main air compressor or compressors to the primemover. The disadvantage of this arrangement is that an oversizecompressor must be utilized to provide at all times suflicient air whenthe main prime mover is running at idling speed. A further disadvantageis the serious tendency of such a compressor to pass large quantities ofoil into the air brake system. It is therefore desirable to utilizemotor-driven air compressors in diesel-electric or gas turbine-electriclocomotives, and it is further desirable to provide a system having twocompressors so that only one need function during normal air demand,with an additional compressor being available for increased demand.There are, however, special problems involved in such an'app-lication byvirtue of the limited availability of power in such a self-containedmotive power unit. It is therefore further desirable to provide a simplearrangement for holding 011 the compressor load for a short period oftime when starting the compressors until the motor torque has had achance to build up. Without such an arrangement, unduly large sizemotors would have to be used to start the loaded compressor, with anaccompanying heavy drain on the electrical power system.

It is therefore an object of this invention to provide an improvedcompressed air supply system having an arrangement for unloading thecompressor during starting.

A further object of this invention is to provide an improved compressedair supply system having two compressors with means for unloading thecompressors during starting and in which only one compressor operatesduring normal air demand.

Further objects and advantages of this invention will become apparentand the invention will be better understood by reference to thefollowing description and the accompanying drawing,

and the features of novelty which characterize this invention will bepointed out with particularity in the claims annexed to and forming a,part of this specification.

In accordance with this invention, there is provided a, main compressedair reservoir with a motor-driven compressor connected thereto.

Means responsive to the air pressure in the main mined lower level, andfor stopping the motor when the main reservoir air pressure rises abovea predetermined upper level.

The compressor is provided with unloading means, such as an arrangementto hold the inlet valves open, the unloading means being actuated by airpressure. Means, such as a solenoid valve energized through the pressureresponsive switch is provided to connect the compressor unloading meansto the main reservoir responsive to the predetermined upper pressure,and to connect the unloading means to the atmosphere responsive to thepredetermined lower pressure. Throttling means, such as a check valve,is provided on the atmospheric side of the solenoid valve and anotherair reservoir is connected to the unloading means. A bypass check andchoke means is provided arranged to admit air slowly to the second airreservoir from the main reser voir when the compressor unloading meansis connected to the main reservoir, and to release air from the secondreservoir to the unloading means when the unloading means is connectedto the atmosphere. The air throttling means is arranged slowly todischarge the air released from the second reservoir to the atmosphereso that air pressure from the second reservoir is maintained for a shortinterval of time on the unloading means, so that the compressor isunloaded for starting the motor. If the system includes two compressors,the pressure responsive switch of one of the compressor units is ar-'ranged to respectively start and stop its associated motor at lower andupper air pressures respectively lower than the pressures at which theswitch of the other compressor unit will start and stop its associatedmotor, so that only one compressor will operate during normal airdemand.

In the drawing, Fig. 1 is a schematic illustration of the improvedcompressed air supply system of this invention; and Fig. 2 is a view incross-section of the compressor unloading device utilized in thissystem.

Referring now to the drawing, there is shown a main compressed airreservoir I which is fed by compressors 2 and 3 through line s. Thecompressors 2 and 3 are respectively driven by electric motors 5 and 6in any suitable manner, as by belt drives 1. A compressed air supplyline 8 discharges from the main reservoir I, and another line 9branching off therefrom feeds air from the main reservoir l to pressureresponsive switches It and l I. The pressure switches I ii and H arerespectively provided with first contacts l2 and I3 arranged torespectively connect motors 5 and 6 for energization from lines l4 andI5, which in turn are connected to a suitable external sourceof power(not shown).

Each of the compressors 2 and 3 is respectively provided with anunloading device It as shown 3 in detail in Fig. 2. Referring now toFig. 2, there is shown the end wall I! of the compressor cylinder, withair inlet valves I3 arranged therein. A casing I9 is arranged over theair inlet valves I8, defining a cavity 29 communicating with the airinlet valves and an air inlet opening 2! is formed in the wall of thecasing I9 for admitting air to the cavity 29 and thence to thecompressor through the air inlet valves I9. A cylinder 22 is formed onthe upper surface of the casing I9 with a piston 23 arranged therein.Line 29 communicates with the cylinder 22 and piston 23 is connected toa diaphragm member 25 having fingers 26 depending therefrom. A spring 27is arranged between the diaphragm member 29 and a seat 28 to bias thepiston 23 and member 25 away from the inlet valves I2. It will bereadily seen that when compresed air is admitted to cylinder 22 throughthe inlet pipe 22, the piston 23 will move downwardly against the spring23, causing the fingers 26 to hold open the inlet valves I8, which arenormally biased closed by means of suitable springs 28.

Referring again to Fig. l, the compressor unloading devices 56 areconnected to the line 9 by means of unloading lines 29 and 36respectively. Solenoid valves 3! and 32 are respectively arranged in thelines 29 and 3G and are respectively 7 provided with operating coils 33and 32, the operating coils 33 and 34 being respectively connected forenergization from the power lines Id and I5 through contacts 35 and 35of pressure responsive switches I and I I. Each of the solenoid switches3| and 32 is provided with a spool 3'3, only the solenoid switch 3|being here shown in cross-section, it being understood that switch 32 isidentical in construction. When the operating coils 33 and 34 are notenergized, the spools 3? respectively open the lines 29 and 39 and whenthe solenoid switch operating coils are energized, the spools 31 areshifted, closing the lines 29 and as so they no longer communicate withline 9, and connecting the lines 29 and 39 to discharge lines as and 39respectively. Adjustable choke valves 29 and ii are arranged on the endsof the discharge lines 38 and 39, the choke valve 42 being shown incross section. Volume reservoirs 42 and 43 are provided connected to thelines 29 and 3G by lines 44 and 45, in which bypass check and chokevalves 55 and 41 are arranged; valve as being shown in cross-section.

in operation, considering only the system associated with compressor 2and assuming that the main air reservoir I is fully charged to therequired pressure, for example, 140 1b., the pressure responsive switchIi] will have opened the contacts I2 and the motor will therefore beshut off. Since the contacts 35 of switch IE will also be open, theoperating coil 33 of solenoid valve 3i will not be energized and thespool 3'! will not be picked up. The unloading device I6 of thecompressor 2 will therefore be connected to the main reservoir I through1 lines 8, 9 and 29, and the main reservoir air acting on the piston 23will cause the member 25 and fingers 26 to open the air inlet valves I8,thus preparing the compressor for the next starting cycle. During thisperiod, the volume reservoir 42 has been relatively slowly charged fromthe main reservoir I through therestricted bypass check and choke valve46.

As the pressure in the main reservoir I drops due to normal usage, suchas applying and releasing the air brakes, blowing the horn, etc., a"predeterm'ined lower pressure'will be reached, for 'ex-,

ample, 130 lb.,which'will cause the 'pressu'rer'esponsive switch I9 toclose the contacts I2 and 35.

Closing the contacts I2 will start the motor 5 and compressor 2, andsince the air inlet valves i8 were held open by reason of main airpressure being applied to the unloading device It, the compressor willstart sucking air in through the entrance 2I and the valves 53, anddischarging it back through the same valves and opening. Consequently,the compressor does no work except for the friction and windage lossesduring this period. The closing of the contacts 35 energizes theoperating coil 33 of solenoid valve 3|, picking up spool 31. This closesoff the main reservoir air from the compressor unloading device IB andconnects the line 29 to discharge line 33. The air pressure in thevolume reservoir 42 now exerts pressure on the unloading device It tohold the inlet valves I8 open. In the meantime, the air from the volumereservoir :32 is exhausted to the atmosphere through discharge line 38and choke valve 49 at a controlled slow rate. After a certain period oftime, for example, 3 to 4 seconds, suificient to allow the motor 5 tostart, sufiicient air will have been vented out of the line 29 throughdischarge line 38 and choke valve 4!} to permit the piston 23 anddiaphragm 25 of the unloading device I6 to raise, permitting the inletvalves I8 to close. The valves then function normally so that thecompressor will pump air in the normal manner.

The compressor is now functioning normally to again charge up the mainair reservoir I. As the pressure in the reservoir I builds up to the topsetting of 14 0 1b., the pressure responsive switch III will againoperate, opening the contacts 35 and I2, shutting off the motor 5, andde-energizing the operating coil 35 of solenoid valve 3|. Whendeenergized, the spool 31 of solenoid valve 3| returns to its normalposition as shown in Fig. l, disconnecting the line 29 from dischargeline 38 and connecting it again to line 9 so that the main reservoir airagain passes into the unloading device It to open the inlet valves I8.The 'compressor is then prepared for another time delay starting cycle,and the volume reservoir 42'is again slowly charged with main reservoirair through the bypass check and choke valve 46.

It will be readily understood that the operation of the system andcomponents connected to compressor 3 is identical to that describedabove in connection with compressor 2. In order to have one compressoronly operate during normal demand, it is merely necessary to set thedrop-out and pick-up ranges of one of the pressure responsive switchesI9 and II lower than the corresponding ranges of the other switch. Forexample, the switch IO of compressor 2 may be set to drop out at a highpressure of 140 lb. and "to pick up at a low pressure of 130 1b., andthe switch I I of compressor 3 may be set to drop out at a high pressureof 135 lb. and to pick up at a low pressure of lb. Thus, during normalair demand on the locomotive air system, only compressor 2 willfunction. For example, with normal air demand, if the pressure fallsslightly below 1b., but not to 125 1b., only compressor 2 will start.However, assuming greatly increased air demand, as for example when allbrakes are applied. the'air pressure in the reservoir I may rapidly fallbelow 125 1b., so that both compressors are started. Compressor 3 willthen out out when lb. pressure is reached, and compressor 2 will cut outwhen the upper level of lb. is reached.

It will now be readily apparent that this inn n q ide m ve com e se 1ply system and in particular an improved arrangement for unloading thecompressors for starting. In addition, this system provides a simplearrangement to utilize only one compres sor during normal air demand.

While I- have shown-and described a particular embodiment of thisinvention, further modifications and improvements will occur to thoseskilled in the art. I desire it to be understood, therefore, that thisinvention is not limited to the form shown, and I intend in the appendedclaims to cover all modifications which do not depart from the spiritand scope of this invention.

What I claimas new and desire to secure by Letters Patent of the UnitedStates is:

1. A compressed air supply system comprising amain compressed airreservoir adapted to have a compressed air supply line connectedthereto. a compressor connected to supply compressed air to said mainreservoir, an electric motor connected to drive said compressor, meansresponsive to the air pressure in said main reservoir for starting saidmotor when said main reservoir air pressure falls below a predeterminedlower level and for stopping said motor when said main reservoirpressure rises above a predetermined upper level, means responsive toair pressure for holding open the inlet valve of said compressor tounloadsaid compressor, means for connecting said holding means to saidmain reservoir responsive to, said predetermined upper pressure and tothe atmosphere responsive to said predetermined lower pressure, meansfor throttling air on the atmospheric side of said connecting means,another air reservoir connected to said holding means, and meansarranged to admit air slowly to said other air reservoir from said mainreservoir when said holding means is connected to said main airreservoir and to release air from said other reservoir to said holdingmeans when said holding means is connected to the atmosphere, said airthrottling means being arranged slowly to discharge the air releasedfrom said other reservoir to the, atmosphere whereby air pressure fromsaid other reservoir is maintained for a short interval on said holdingmeans to unload said compressor for starting said motor.

2. A compressed air supply system comprising a main compressed airreservoir adapted to have a compressed air supply line connectedthereto, a compressor connected to supply compressed air to said mainreservoir, an electric motor connected to drive said compressor, switchmeans operable responsive to the air pressure in said main reservoir andconnected in circuit with said motor for starting said motor when saidmain reservoir air pressure falls below a predetermined lower level andfor stopping said motor when said main reservoir air pressure risesabove a predetermined upper level, unloading means on saidcompressor'operable in response to air pressure arranged to hold openthe inlet 'valve of said compressor, valve means arranged to connectsaid unloading means to said main'reservoir responsive to saidpredetermined upper pressure and to a discharge line responsive to saidpredetermined lower pressure, air choking means in said discharge line,another air reservoir connected to said unloading means, and bypasschecking and choking means connected between said other air reservoirand said unloading means and arranged slowly to admit air to said otherreservoir from said main reservoir when said unloading means isconnected to said main reservoir and to release air. from said other airreservoir to said unloading means when said unloading means is connectedto said discharge line, said air choking 6 means being arranged slowlyto discharge to the atmosphere the air released from said otherreservoir whereby air pressure from said other reservoir is maintainedon said unloading means for a short interval to unload said compressorfor starting said motor.

3. A compressed air supply system comprising a main compressed airreservoir adapted to have a compressed air supply line connectedthereto,

a compressor connected to supply compressed air to said main reservoir,an electric motor con-- nected to drive said compressor, switch means:operable responsive to the air pressure in said. main reservoir andconnected in circuit with said.

motor for starting said motor when said main reservoir air pressurefalls below a predetermined lower level and for stopping said motor whensaid main reservoir air pressure rises above a predetermined'upperlevel, unloading means on said compressor operable in response to airpressure arranged to hold open the inlet valveof said compressor, valvemeans operable responsive to operation of said switch means and arrangedto connect said unloading means to said main reservoir responsive tosaid predetermined upper pressure and to a discharge line responsive tosaid predetermined lower pressure, air choking means in said dischargeline, another air reservoir connected to said unloading means, andbypass checking and choking means connected between said other airreservoir and said unloading means and arranged slowly to admit air tosaid other air reservoir from said main reservoir when said unloadingmeans is connected to said main reservoir and torelease air from saidother air reservoir to said unloading means when said unloading means isconnected to said discharge line, said air choking means being arrangedslowly to discharge to the atmosphere the air released from said otherair reservoir whereby air pressure from said other reservoir ismaintained on said unloading means for a short interval to unload saidcompressor for starting said motor.

4. A compressed air supply system comprising a main compressed airreservoir adapted to have a compressed air supply line connectedthereto, a compressor connected to supply compressed air to said mainreservoir, an electric motor connected to drive said compressor, apressure responsive switch connected to said main reservoir and operableresponsive to the air pressure therein, said switch being connected incircuit with said motor and arranged to start said motor when said mainreservoir air pressure falls below a predetermined lower level and tostop said motor when said main reservoir air pressure rises above apredetermined upper level, said compressor having an unloading deviceoperable in response to air pressure and arranged to hold open the airinlet valve of said compressor to unload the same, anunloading lineconnecting said main reservoir to said device for supplying air thereto,a two-way solenoid valve having its operating coil connected forenergization through said switch, said valve being connected in saidline and arranged to open the same responsive to said predeterminedupper pressure and to close said line and connect said unloading deviceto a discharge line responsive to said predetermined lower pressure, achoke valve in said discharge line, another air reservoir connected tosaid unloading device by a third line, and a bypass check and chokevalve in said third line arranged slowly to admit air to said otherreservoir from said main reservoir when said unloading line is open, andto restraits legalseQ-air from said other reservoir to said unloadingdev-ice when said unloading device isconnectedtosaid discharge line,said choke valve being; arranged slowly to discharge to the at- I:mosphere the air released from said other reservoir whereby airpressure from said other reservoir is maintained on saidunloadingdevicefor a ;short interval to unload said compressor for .starting saidmotor.

-.v A compressed air supply system comprising :a comprese'd' airreservoir adapted to have a compressed air supply line connectedthereto, and a 'pfair of'compre'ssor units each comprising a compressor.connected to supply compressed ai'r to said main reservoir, an electric'motor connected to drive said compressor; means responsive to the air;pressure in" said main reservoir for startingsaid motor'wh'en: said mainreservoir air pressure falls below: apredetermined lower level and forstopping said: motor when-said main reservoirair pressure rises aboveapredetermined upper'l'evel, means responsive to air pressure fornoldingopen the inlet valve of said compressor'to unload saidcompressor, means for connecting said holding means to saidm'ainreservoir responsive to said predetermined upper pressure and to theatmosphere responsive to said predetermined lower pressure, means forthrottling air on the atmos'pheric side of said connecting means,another air reservoir-connected to said holding means, and

' irieaiisarranged'to admit air slowly to saidother air reservoir from'said mam-reservoir when said holding means is connected to said mainair reservoirand to release air'fronisaidother' reser voir to saidholding means-when'said holding means is connected to the atmosphere,said air throttling means being arranged slowly todischarge'the ai-rreleased from said other re'se'rvoir toth'e atmosphere .whereb'y' airpressure'froni said other reservoir'is maintained for a short intervalon: said holding means to umoadsaid compressor for starting said motor,said tstarting means of one of said units being arranged respectively tostart-andstop"- its associated motor at'upper-and lower air'pressurelevels respectively lower than the pressure levels at which the startingmeans ofth'eotherof said units respectivelystarts and stops itsassociated motor so thatonly one compressor unit operates during normalair demand.

6.: A compressed air supply systemcomprising acompressed air reservoiradapted to have I a compressed air supply line connected thereto, and apair of compressor units each comprising a compressor connected tosupply'compre'ss'ed air to said main reservoir, an electric motorconnected to drive said compressor, a pressure responsive switchconnected to saidmain res'ervoir-and op erable responsive to the airpressure therein; said switch being connected in circuit with said motorand arranged to start said motor when'sa'id main reservoir air pressurefalls below apredete'rm'in'ed lower level and to stop-said motor whensaid main reservoirairpres'sure rises-above a predetermined upper level,said compressor having a'n unloading device operable in response to airpressure and arranged to hold open the air inlet valve of i saidcompressor to unload the sam'e, an unloading line connecting said mainreservoir to said' device for supplying air thereto, a two way solenoidvalve having its operating coil connected for energization through'saidswitch, said valve being con-- nected in said lineand arranged to openthe same responsive" .to said; predetermined upper pres sure-f and:v to4 close' saidf lineand connect said un" loading device to a dischargeline responsive to said predetermined lower pressure, a choke valve insaid discharge line, anothe r air reservoir connected to saidunloadingdevice by a third line, and a bypass check and choke valve insaid third line arranged slowly to admit air to said other reservoirfrom said main reservoir when said un-, loading line is open and torelease air from said other reservoir to said unloading device when saidunloading device iscon'nected to said, discharge line, said choke valvebeing arranged slowly to discharge to the atmosphere the air releasedfrom said other reservoir whereby air pressure from said: otherreservoir is maintained on said unloading device for a short interval tounload said compressor for starting said motor, said pressure responsiveswitch of one of said units being arranged respectively to'start andstop its; associated motor at upperand' lower air pressurelevelsrespectively lower than the air pressure levels at which thepressure responsive switch of the other of said units respectivelystarts and stops its associated motor so that only one compressor unitoperates during normal air demand.

7. A compressed air supply system comprising a main compressed airreservoir, a compressor connected to supply compressed air to said mainreservoir, an electric motor connected to drive said compressor, meansresponsive to the air pressure in said main reservoir for starting saidmotor when said main're'se'rvoir air pressure falls below apredetermined lower" level and for stoppingsaid motor when said mainreservoir air pressure rises above a predetermined upper level, meansoperable in response to air pressure for unloading said compressor,means for connecting said unloading means to said main reservoirresponsive to said predetermined upper pressure and to the atmosphereresponsive to said predetermined lower pressure, means for throttlingair on the atmosphere side of said connecting means, an-

other air reservoir connected to said unloading means, and meansarranged toadmit air slowly to said other airrese'rvoir from said mainreservoir when said unloading means is; connected to saidmainairreservoir and to 'relea'se'air from said'other reservoir "to saidunloading'means when said unloading'mean's is" connected to theatmosphere, said air throttling means being arranged slowly to dischargethe air released from said other reservoir to the atmosphere whereby airpressure from said other reservoir is' maintained' for a shortintervahon said unloading means to unload'said compressor for startingsaid ROGER MCINTYRE.

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